BG Flashcards
What are the structures of the basal ganglia?
-structures that yield distinctive kinds of mvmd disorders when damaged:
Striatum
-caudate + putamen
Globus pallidus
-interna and externa
sub thalamic nucleus
substantia nigra
-compact and reticular parts
What is the major outflow pathway to the thalamus from the BG?
globus pallidus
reticular substantia nigra (less so)
What are the general features of BG related mvmt disorders?
involuntary movements, hyperkinetic disorders (chorea, athetosis, ballismus)
difficulty initiating mvmt
general increase in flexor/extensor tone, can cause rigidity and abnormal fixed posture (dystonia)
What are the two main diseases discussed in relation to the BG?
huntington’s and parkinson’s
What degrades when you have huntingtons?
stratum (caudate and putamen)
What are the two outflow pathways of the globus pallidus?
ansa lenticularis
lenticular fasciculus
What are the two parts of the substantia nigra and what do they do?
compact part: sends dopaminergic projections to striatum
reticular part: basal ganglia output nucleus
What are the four basic circuits of the basal ganglia?
motor loop: learned mvmts
cognitive loop: motor intentions
limbic loop: emotional aspects of mvmt
oculomotor loop: voluntary saccades
Can the basal ganglia initiate mvmts?
NO but it is active during all mvmts
What does the BG motor loop do?
influences descending motor pathways by scaling strength of muscle contractions, organizes order of mvmts needed with the supplemental motor area.
mostly involves putamen
What does the BG cognitive loop do?
mostly involves caudate
motor learning, planning mvmts ahead of time….but after a mvmt is learned the motor loop (putamen) takes over
Describe the path of the cognitive loop
prefrontal cortex > caudate > globus pallidus > VA of thalamus > prefrontal cortex
What does the BG limbic loop do?
gives expression to emotions (smiling, gestures, aggression etc)
Describe the path of the limbic loop
inferior prefrontal cortex > ventral striatum (aka nucleus accumbens) > ventral pallidum > DMN of thalamus > interior prefrontal cortex
What does the oculomotor loop do?
voluntary saccades, disinhibits the superior colliculus
he did not talk about this shit much
is the reticular part of the substantial nigra active or inactive when the eyes are fixed on an object?
active
What makes up the thalamic fasciculus?
ansa lenticularis
lenticular fasciculus
(GP to thalamus)
You have a three neuron circuit:
- excitatory neuron
- inhibitory neuron
- spontaneously firing neuron
What happens to neuron 3?
it is silenced
You have the same three neuron circuit as before, but a new neuron has been added:
- excitatory neuron
2a. inhibitory neuron
2b. inhibitory neuron - spontaneously firing neuron
What happens to neuron 3?
neuron 3 is released and it fires an action potential (disinhibition)
Describe the direct pathway of the BG motor loop.
- Excitatory neurons leave the cerebral cortex and synapse on the striatum
- The striatum sends out inhibitory neurons to the globus pallidus internus (GPI)
- The GPI sends out inhibitory neurons to the thalamus via the thalamic fasciculus (but ‘less’ inhibitory than usual to the thalamus, because the striatum has inhibited the GPI so it is less active)
- The thalamus is disinhibited, so it sends out excitatory neurons to the cortex and increases voluntary movements
Does the direct pathway of the motor loop increase or decrease cortical output?
increases cortical output (more mvmt)
Describe the indirect pathway of the BG motor loop.
- Excitatory neurons leave the cerebral cortex and synapse on the striatum
- The striatum sends out inhibitory neurons to the globus pallidus externa (GPE)
- The GPE sends out inhibitory neurons to the subthalamus
- The subthalamus sends out excitatory neurons to the GPI
- The GPI sends out inhibitory neurons to the thalamus via the thalamic fasciculus. Now the thalamus is inhibited more than usual, because the subthalamus has turned on the GPI more than usual.
- Decreased excitatory output from the thalamus to the cortex
- Decreased cortical output
Does the indirect pathway of the motor loop increase or decrease cortical output?
decreases cortical output to suppress unwanted movements
What happens if you damage your subthalamus?
your indirect pathway will get fucked up so you will have a lot of involuntary movements happening
called hemiballismus
Are the putamen and globus pallidus somatotopically arranged?
YES
important because the direct pathway can stimulate movement in one are while the indirect pathway can suppress unwanted movements simultaneously in a different area
What is the relationship between substantial nigra and the direct motor pathway?
striatal projection neurons to the GPI have D1 receptors, which are facilitatory
(i think these receptors help to inhibit GPI more, so the thalamus is less inhibited)
this makes the supplemental motor area active prior to mvmts occurring (who the fuck knows)
What is the relationship between substantial nigra and the indirect motor pathway?
stratal projection neurons to the GPI have D2 receptors, which are inhibitory
(aka the keep the GPI more turned on so the thalamus is more inhibited)
What are the three cardinal features of parkinson’s disease?
bradykinesia (slow mvmt)
resting tremor
rigidity
What are lewy bodies?
found in the substantial nigra, they ‘plug’ dopamine receptors and give you parkinsons booooo
What motor pathway is favored in parkinson’s disease and why?
the indirect pathway is favored (decreased cortical output — bradykinesia)
this is because the striatum is not receiving any dopamine projections from the compact SN. This causes the striatum to over inhibit the GPE. consequently, the subthalmus is underhibited by the GPE. the subthalamus then overexcites the GPE, causing the thalamus to be over inhibited. decreased thalamic outputs to cortex, decreased movements.
How does levodopa work?
tries to replace dopamine
What is a pallidotomy?
possible treatment for parkinsons, you destroy the globus paladus in an attempt to increase cortical outputs and treat bradykinesia
What side of the body would a right sided pallidotomy affect?
left side of body
